Exemplary embodiments of the invention relate to an exhaust gas system for exhaust gas routing and exhaust gas aftertreatment in a motor vehicle.
Exhaust gas systems of the kind addressed here are generally used for routing the exhaust gas within an exhaust gas train of an internal combustion engine and for aftertreatment of the exhaust gas, in particular for reducing a particulate and/or harmful substance concentration. Typically, in particular for reducing nitrogen oxides, reducing agents in an initial liquid state, such as mineral oil fuel or an aqueous urea solution, are injected into the exhaust gas flowing through the exhaust gas system. In order to obtain an efficient reduction of hazardous substances and a chemical reaction that is as complete as possible, it is necessary to vaporize the reducing agent and distribute it is uniformly as possible in the exhaust gas flow. If an aqueous urea solution is used, the urea must be converted to ammonia by means of hydrolysis and/or thermolysis so that a selective catalytic nitrogen oxide reduction can be subsequently carried out.
An exhaust gas system, which has a first exhaust gas duct element with an inlet opening and an outlet opening, is disclosed in European patent application EP 2 128 398 A1, wherein the first exhaust gas duct element is in the form of an outlet funnel of a particulate filter. A second exhaust gas duct element has a transfer pipe with a longitudinal axis and a sleeve surface. This projects into the outlet opening of the first exhaust gas duct element and the end thereof projects into the outlet opening rests closely against a wall of the first exhaust gas duct element, thus closing the first end. A multiplicity of intake openings, which are formed as a rectangular slot and are distributed uniformly—viewed in the circumferential direction—over the sleeve surface, are provided in the sleeve surface adjacent to the closed end. The transfer pipe therefore has intake openings along its entire circumference adjacent to the first closed end. It is accommodated in the first exhaust gas duct element by means of its closed end and the intake openings so that exhaust gas flowing in through the inlet openings in a first direction can flow into the transfer pipe through the intake openings. The exhaust gas then flows—viewed in the direction of the longitudinal axis of the transfer pipe—in the transfer pipe, through the outlet opening and out of the first exhaust gas duct element. An injector unit for introducing a reducing agent into the exhaust gas flow is provided at the first exhaust gas duct element.
Here, it can be seen that the longitudinal axis of the transfer pipe is arranged parallel to the first direction in which exhaust gas flows through the inlet opening into the first exhaust gas duct element. Therefore, in order to pass from the inlet opening into the transfer pipe and through this through the outlet opening, the exhaust gas must be deflected by substantially 180°. In particular, the exhaust gas must initially be deflected by substantially 90°—starting from the inlet opening—to be able to flow into the intake openings. A further deflection by substantially 90° then takes place in the transfer pipe. A relatively intricate flow path for the exhaust gas is formed in this way and is associated with a pressure loss. A swirling of the exhaust gas formed in the transfer pipe, which mixes the injected reducing agent with the exhaust gas, has a reduced swirl rate, as the exhaust gas has already lost kinetic energy due to the first 90° deflection from the inlet opening to the intake openings. It can also be seen that the injector unit is arranged such that the reducing agent is injected into the transfer pipe downstream of the intake openings. For this reason, a mixing section arranged downstream of the intake openings for vaporizing and mixing reducing agent with the exhaust gas must be made comparatively long, which has a detrimental effect on the installation length of the second exhaust gas duct element and therefore also the exhaust gas system as a whole.
Exemplary embodiments of the invention are therefore directed to an exhaust gas system with an increased swirl rate making optimum use of the kinetic flow energy of the exhaust gas and a comparatively compact design with a shortest possible mixing section.
As the longitudinal axis of the transfer pipe lies substantially perpendicular to the first direction in which the exhaust gas flows through the inlet opening into the first exhaust gas duct element, it is possible for the inflowing exhaust gas to pass from the inlet opening into the intake opening without deflection, in particular without 90° deflection. This substantially prevents a loss of kinetic energy in the exhaust gas flow, thus enabling an exhaust gas swirl with high swirl rate to be established when the exhaust gas flows into the transfer pipe. As the reducing agent can be injected by the injector unit into the first exhaust gas duct element upstream of the intake opening, early injection takes place—viewed in the flow direction—thus enabling the mixing section to be optimally utilized, particularly in the transfer pipe. At the same time, the reducing agent vaporizes, preferably at least partially, before entering the transfer pipe. Together with the highly efficient swirl with high swirl rate, this results in rapid vaporization and mixing of the reducing agent with the exhaust gas, as a result of which hydrolysis and/or thermolysis of urea is accelerated. The mixing section itself can therefore be made shorter than in the known exhaust gas system, which has an advantageous effect on the length of the second exhaust gas duct element and therefore also the exhaust gas system as a whole.
Preferably, the intake opening is connected directly to the closed end of the transfer pipe and is therefore—viewed in the longitudinal direction—not spaced apart therefrom or only spaced apart therefrom to a small extent. However, it is possible for the intake opening to be at a short distance—compared with its longitudinal extension—from the closed end.
The transfer pipe therefore projects into the outlet opening such that the intake opening is completely arranged in the first exhaust gas duct element. In doing so, it is made a short as possible and it therefore preferably extends not very much further into the first exhaust gas duct element than a longitudinal extension of the intake opening. From this, it also follows that—measured in the longitudinal direction—a distance from the closed end of the transfer pipe to the intake opening is made as small as possible in order not to extend the length of the transfer pipe projecting into the first exhaust gas duct element unnecessarily and to avoid dead zones for the exhaust gas flow.
The transfer pipe is preferably accommodated in the outlet opening in an interlocking manner. Accordingly, an edge of the outlet opening encompasses the transfer pipe with a matching contour and with a complementary shape, in a close-fitting and preferably sealing manner, so that no exhaust gas can escape from the first exhaust gas duct element between an edge of the outlet opening and the sleeve surface of the transfer pipe. Particularly preferably, the transfer pipe is additionally joined to the first exhaust gas duct element in the region of the outlet opening by substance-to-substance bonding, preferably welded. This results in a particularly well sealed connection. All the exhaust gas flowing into the first exhaust gas duct element through the inlet opening must therefore flow via the intake opening and through the transfer pipe out of the first exhaust gas duct element, as there is no other outgoing flow path therefrom.
With the help of the injector unit, preferably, an aqueous urea solution is injected into the exhaust gas flow, wherein the urea is converted to ammonia in the mixing section by means of hydrolysis and/or thermolysis. In this case, a catalytically active element, in particular a catalytic converter for carrying out a selective catalytic reduction, which converts nitrogen oxide with the ammonia to form elementary nitrogen and water, is preferably provided after the mixing section. However, in an exemplary embodiment of the exhaust gas system, it is also possible for a different reducing agent, which in the initial state is preferably liquid, such as a mineral oil fuel for example, to be injected into the exhaust gas flow.
Preferably the exhaust gas system includes transfer pipe that is cylindrical at least in the region of the intake opening. Preferably, the cylindrical geometry has an oval base surface so that—viewed in cross-section—the transfer pipe is oval in shape. As a result of the intake opening, which is preferably arranged centrally in the oval transfer pipe, inflowing exhaust gas forms a double vortex, as a result of which a particularly efficient mixing of the reducing agent injected into the exhaust gas flow can be effected. Preferably, the geometry of the transfer pipe is chosen such that two opposing exhaust gas flow vortices are formed with—viewed in cross-section—approximately circular progression. In this case, the vortices are particularly stable. They are therefore preferably also maintained over a whole length of the mixing section.
In another exemplary embodiment, it is possible for the transfer pipe to have a cross-sectional form corresponding to two circular segments placed adjacent to one another. In this case too, it is possible, particularly when the intake opening is arranged centrally, to form a stable double vortex in the transfer pipe that is maintained over a length of the whole mixing section. The length of the mixing section is preferably at least 200 mm to 300 mm or even more.
In yet another exemplary embodiment, it is possible for the transfer pipe to be formed cylindrically with a circular base surface. In this case, the intake opening is preferably arranged off center and in particular such that the exhaust gas flows into the transfer pipe tangentially. This then forms a stable single vortex, as a result of which good mixing of the reducing agent with the exhaust gas is likewise achieved.
If the transfer pipe—viewed in cross-section—is in the form of an oval, a ratio of a longer cross-sectional axis to a shorter cross-sectional axis is at least 1.5 up to a maximum of 2. If the exhaust gas system is used in conjunction with an internal combustion engine of a motor vehicle, the capacity of which lies in the range from approximately 1.6 liters to 3.5 liters, the length of the shorter cross-sectional axis is preferably at least 30 mm up to a maximum of 100 mm. Exemplary embodiments with different dimensions or ratios are, of course, possible.
Also preferred is an exhaust gas system in which the transfer pipe has only one intake opening. This is arranged facing away from the inlet opening of the first exhaust gas duct element so that the exhaust gas flowing in through the inlet opening must initially flow around the transfer pipe before then being able to flow into the transfer pipe through the intake opening, effectively in the opposite direction to the inlet direction. As a result of the flow reversal of the transfer pipe, the exhaust gas is already endowed with a swirl and flows into the transfer pipe with a tangential speed component. Particularly preferably, the exhaust gas flow flows around the transfer pipe on both sides and, in this respect, is divided into two partial flows, which—viewed in the flow direction—flow past the transfer pipe to right and left and meet one another behind it in the region of the intake opening. The partial flows passing into the transfer pipe therefore have tangential speed components pointing in opposite directions so that a very stable double vortex is formed in a particularly efficient manner and with high swirl rate.
Here, preferably, a wall of the first exhaust gas duct element is curved inwards in the region of the closed end of the second exhaust gas duct element such that it seals tightly with the closed end. This prevents exhaust gas from being able to flow beyond the closed end of the transfer pipe and in this way passing to the intake opening. The whole of the exhaust gas flow must therefore flow around the transfer pipe to the intake opening, which increases the stability and swirl rate of the vortex formed, in particular of the double vortex.
The intake opening preferably has a larger extension in the direction of the longitudinal axis of the transfer pipe than perpendicular thereto. It is therefore elongated—viewed in the longitudinal direction—wherein the ratio of a longitudinal extension to a transverse extension of the intake opening is preferably at least 1.5 to a maximum of 4. Particularly preferably, the intake opening is in the form of a slot with substantially rectangular penetration area. Here, the ratio of the long side of the rectangle to the short side of the rectangle is preferably at least 1.5 to a maximum of 4. It is possible for the substantially rectangular penetration area to be rounded in the region of the corners. In particular, the shape of a rectangular slot for the intake opening enables a particularly stable formation of a double vortex of the exhaust gas flow in the transfer pipe.
The intake opening preferably extends over the whole length of the transfer pipe projecting into the first exhaust gas duct element, i.e., from an inner side of the outlet opening to the closed end. The shorter transverse dimension of the intake opening is preferably less than the shorter cross-sectional axis of the oval transfer pipe.
Also preferred is an exhaust gas system in which the first exhaust gas duct element is in the form of an outlet funnel of an oxidation catalytic converter. Particularly preferably, the inlet opening effectively overlaps an outlet side of the oxidation catalytic converter, so that the first exhaust gas duct element is arranged at an output of the oxidation catalytic converter in the form of an exhaust gas manifold element. The exhaust gas system is therefore preferably formed overall such that the transfer pipe projects into the outlet funnel of the oxidation catalytic converter. The mixing device formed by the injector unit and the transfer pipe is therefore also arranged downstream of the oxidation catalytic converter, preferably flanged thereto.
Also preferred in this regard is an exhaust gas system in which the first exhaust gas duct element is scoop-shaped. Here, an imaginary plane defined by the inlet opening, namely an imaginary plane perpendicular to which the flow direction of the exhaust gas through the inlet opening lies, is oriented substantially, preferably exactly, perpendicular to an imaginary plane defined by the outlet opening, namely an imaginary plane perpendicular to which the exhaust gas flow through the outlet opening lies. A diversion of the exhaust gas flow by substantially, preferably exactly 90°, therefore takes place from the inlet opening to the outlet opening. At the same time, the first exhaust gas duct element overlaps the transfer pipe projecting into it. As a result, the arrangement of the first exhaust gas duct element and the second exhaust gas duct element overall effectively has the shape of an air scoop. The 90° deflection of the exhaust gas flow occurs substantially when the exhaust gas flows into the transfer pipe, where, starting from the intake opening, it impinges against a wall of the transfer pipe arranged opposite, wherein, on the one hand, the vortex, in particular double vortex, is formed, and wherein, on the other, the exhaust gas flow is deflected by 90°, as the transfer pipe is closed at its first end which projects into the exhaust gas duct element.
Preferably, the first exhaust gas duct element has a flow chamber which—viewed in the first direction—with regard to the transfer pipe is arranged before the intake opening and faces away from the inlet opening. This means that—viewed in the flow direction of the exhaust gas from the inlet opening—a flow chamber, in which the exhaust gas, which flows around the transfer pipe, collects in front of the intake opening facing away from the inlet opening before it passes through it into the transfer pipe, is arranged after the transfer pipe. The injector unit is arranged and aligned such that an injection stream thereof is directed into this flow chamber. Here, the term “injection stream” on the one hand refers to the reducing agent injected by the injector unit and, on the other, the emission characteristic of the injector unit, wherein the emission characteristic is substantially conical. Here, the conical stream of reducing agent opens in a direction pointing away from the injector unit. The injection stream, in particular a longitudinal axis of the conical stream, is preferably oriented approximately parallel, at the most at an acute angle, to the longitudinal axis of the transfer pipe and particularly preferably aligned away from the intake opening. Here, the injector unit is preferably fixed to the first exhaust gas duct element in close spatial proximity to the closed end of the transfer pipe, so that the injection stream emerges from a region which is arranged close to the closed end and recedes from the intake opening and the transfer pipe along its propagation direction at a preferably small, acute angle.
Preferably, the injector unit is designed such that it injects a plurality of conical streams, particularly preferably two conical streams, into the flow chamber, wherein the conical streams are arranged one after the other in a direction that is oriented perpendicular to the longitudinal direction of the transfer pipe and parallel to the first direction. At the same time, the longitudinal axis of the rear conical stream—viewed from the transfer pipe in the first direction—preferably has a larger angle to the longitudinal axis of the transfer pipe than a corresponding front conical stream.
In all cases, the reducing agent is injected into the flow chamber formed by the first exhaust gas duct element upstream of the intake opening, that is to say mixed with the exhaust gas flow at a point at which it has not yet entered the transfer pipe and therefore the second exhaust gas duct element. As a result, a comparatively early mixing of the reducing agent with the hot exhaust gas coming from the oxidation catalytic converter takes place. This promotes a vaporization of the reducing agent which, in addition, is mixed particularly efficiently with the exhaust gas flowing into the transfer pipe and forms a swirl, preferably a double swirl. This enables the mixing section to be shortened, and particularly homogenous mixing takes place, which, in particular, is further assisted by forming a double vortex. In doing so, in particular the injection immediately before the intake opening has been shown to be favorable, as an intensive, rapid flow of exhaust gas into the transfer pipe, which carries along, swirls and vaporizes the reducing agent, occurs here.
Also preferred is an exhaust gas system with at least one substantially plate-shaped baffle element, which is fixed to the transfer pipe and/or to the first exhaust gas duct element, is provided in the flow chamber. Preferably, the baffle element is welded to the transfer pipe and/or to the first exhaust gas duct element. At the same time, it is possible for the baffle element to be fixed exclusively to the transfer pipe, preferably welded thereto. It is also possible for the baffle element to be fixed exclusively to the first exhaust gas duct element, preferably welded thereto. Finally, it is possible for the baffle element to be fixed both to the transfer pipe and to the first exhaust gas duct element, preferably welded thereto. The baffle element has a baffle surface facing the injector unit, the normal vector of which is aligned substantially parallel, preferably exactly parallel, to the longitudinal axis of the transfer pipe. At the same time, the baffle element preferably overlaps the intake opening along a direction which is orientated transversely, preferably perpendicular, to the longitudinal axis of the transfer pipe. Ultimately, the baffle element, which is preferably in the form of a baffle plate, is arranged in the flow chamber such that it is impacted at least in certain areas by the at least one injection stream. Reducing agent which impinges on the baffle element preferably bounces off, wherein the drops which bounce off burst into smaller drops and as a result vaporize more quickly.
As a result of the wall contact with a wall of the transfer pipe and/or a wall of the exhaust gas duct element to which it is preferably fixed, the baffle element is heated by thermal conduction. It is also heated by the passing exhaust gas. The baffle element therefore acts as a vaporization element, by means of which vaporization heat is dissipated to the impinging reducing agent. Separate heating of the at least one baffle element is also possible. Preferably, the baffle element also has a temperature above a Leidenfrost temperature of the reducing agent. This guarantees efficient vaporization and also efficient bouncing-off of reducing agent drops on the baffle element.
Preferably, the injection stream impinges on a wall of the first exhaust gas duct element. Here too, drops preferably bounce off and reducing agent is vaporized at the hot wall.
To assist vaporization on the baffle surface of the baffle element, it can have a surface form that preferably comprises pimples. Alternatively or in addition, roughening and/or a coating can be provided. A preferred value for a surface roughness lies in the range from at least 5 μm to a maximum of 50 μm. Preferably, a catalytic coating which supports thermolysis and/or hydrolysis of urea can be provided as the coating. It is also possible to provide a coating which, in addition or alternatively, counteracts the formation of a deposit, in particular by deposition of urea decomposition products. The baffle surface coating preferably includes titanium dioxide, particularly preferably it consists of titanium dioxide.
As the reducing agent at least partially vaporizes due to the contact with the at least one baffle element and/or wall of the first exhaust gas duct element before entering the intake opening of the transfer pipe and/or is fed to a hydrolysis or thermolysis reaction, the efficiency of the mixing section is considerably increased. This can therefore be shortened, as a result of which the exhaust gas system can have a particularly compact form.
The at least one baffle element and/or the injector unit are preferably arranged relative to one another such that the injection stream impinges on the baffle surface with an angle of incidence of preferably less than 45° relative to a normal vector. Particularly preferably, the reducing agent is injected in such a way that it impinges on the baffle surface at least approximately perpendicularly, as a result of which particularly good wetting thereof is achieved.
The at least one baffle element is preferably also aligned substantially parallel to the exhaust gas flow flowing around the transfer pipe and into the intake opening. The at least one baffle element therefore forms a minimal flow resistance for the exhaust gas, so that a pressure loss in the region of the baffle element is minimized or prevented, and as a result of which a vaporization, interaction and mixing of the reducing agent with the exhaust gas in the region of the baffle element is intensified.
Also preferred is an exhaust gas system with a plurality of baffle elements are provided. Particularly preferably, at least three, preferably up to eight baffle elements are provided. Preferably, the baffle elements are arranged one after the other—viewed in the direction of the longitudinal axis of the transfer pipe—and preferably parallel to one another with regard to their baffle surfaces. Accordingly, the normal vectors of the baffle surfaces preferably point at least approximately in the same direction. As a result, it is particularly possible for drops of the reducing agent to bounce off different baffle elements several times, wherein a drop bursts into smaller drops on each impact, thus significantly accelerating the vaporization of the reducing agent.
Also preferred in this context is an exhaust gas system in which the baffle elements each have a cutout in the baffle surface. This is preferably arranged such that the injection stream is directed at the cutout in certain areas. This means that part of the reducing agent emitted by the injector unit passes through the cutout, while another part impinges on the baffle surface surrounding the cutout so that the injection stream is ultimately peeled off by the baffle elements. This results in the formation of a vortex at the edges of the cutouts, which further improves the mixing of the reducing agent with the exhaust gas and the vaporization thereof.
Preferred in this context is an exhaust gas system in which—viewed in the direction of the injection stream—penetration areas defined by the cutouts of the baffle elements reduce along a series of baffle elements. The cutouts have penetration areas for the reducing agent, wherein the penetration area of each cutout of a baffle element reduces from baffle element to baffle element—viewed in the direction of the injection stream. As a result, the injection stream is peeled off to a greater extent from baffle element to baffle element, which improves the formation of vortices at the edges, the bouncing-off behavior, the vaporization behavior and therefore the hydrolysis and/or thermolysis, and finally, the mixing of the reducing agent with the exhaust gas. At the same time, preferably, a depth of the cutouts—measured in a direction perpendicular to a plane defined by the intake opening—reduces from baffle element to baffle element. Preferably, in addition or alternatively, it is provided that a width of the cutouts—measured perpendicular to the depth—also reduces from baffle element to baffle element. In a particularly preferred exemplary embodiment, both the depth and the width of the cutouts—viewed in the direction of the injection stream—reduce along the series of baffle elements.
Also preferred is an exhaust gas system in which the injector unit is arranged and aligned such that the injection stream is symmetrically arranged with respect to a plane of symmetry defined by the first direction and by the longitudinal direction and that divides the intake opening symmetrically. The plane of symmetry is accordingly determined in that both the first direction, that is to say the flow direction of the exhaust gas through the intake opening, and the longitudinal direction of the transfer pipe lie therein. The position of the plane of symmetry is further defined in that it divides the intake opening symmetrically into two equally sized half areas. The injector unit is now arranged and aligned such that the injection stream is also preferably arranged mirror-symmetrically with respect to this plane of symmetry.
In this context, it is also preferred that the at least one baffle element, preferably all baffle elements, are designed and arranged mirror-symmetrically with respect to the plane of symmetry. This results in an overall mirror-symmetrical arrangement of the geometry of the preferably oval transfer pipe, the injector unit, the injection stream and the baffle elements. Particularly when the transfer pipe is oval, this results in a mirror-symmetrical double vortex with respect to the plane of symmetry, wherein, as a result of the likewise symmetrically arranged injector unit, the symmetrical injection stream and the symmetrical baffle elements, a particularly homogenous, uniform distribution of the reducing agent in the symmetrical double vortex is produced. This ensures that the reducing agent is homogenously distributed in the whole exhaust gas flow, thus enabling a hazardous substance concentration to be extensively reduced.
Also preferred is an exhaust gas system in which the intake opening, which faces away from the inlet opening, is designed as a main intake opening which preferably has a larger extension in the direction of the longitudinal axis of the transfer pipe than perpendicular thereto, wherein it is particularly preferably designed as a slotted and substantially rectangular penetration area, and wherein, furthermore, at least one auxiliary intake opening, which—viewed along the first direction—is preferably arranged at the side of the main intake opening, is provided in the sleeve surface of the transfer pipe. The auxiliary intake opening preferably has a smaller penetration cross-section than the main intake opening. At the same time, it preferably has a larger extension in the direction of the longitudinal axis of the transfer pipe than perpendicular thereto. Particularly preferably, it is in the form of a slot with rectangular penetration area. Particularly preferably, both the main intake opening and the at least one auxiliary intake opening are in the form of a rectangular slot, wherein, however, the auxiliary intake opening preferably has a smaller penetration area than the main intake opening. Arranging the auxiliary intake opening at the side enables exhaust gas flowing past the side of the transfer pipe to pass into the transfer pipe. As a result, a pressure loss of the exhaust gas when flowing around the transfer pipe is reduced, as a result of which an installation height—measured in the longitudinal direction—and an installation width—measured in the transverse direction—of the flow channels feeding around the transfer pipe can be reduced. This makes the exhaust gas system more compact. In addition, the auxiliary intake opening assists the formation of the swirl, particularly when the exhaust gas enters the transfer pipe through said auxiliary intake opening as tangentially as possible.
Particularly preferred is an exhaust gas system having two auxiliary intake openings arranged mirror-symmetrically with respect to a plane of symmetry that is defined by the first direction and the longitudinal axis and symmetrically divides the main intake opening and which corresponds to the previously defined plane of symmetry. Auxiliary intake openings, through which the exhaust gas flowing around the transfer pipe can enter the transfer pipe, are therefore provided on the sleeve surface of the transfer pipe to the left and right—viewed in the flow direction of the exhaust gas through the inlet opening. In this way, the pressure loss associated with the circulatory flow is particularly efficiently reduced, which, in turn, enables an additional reduction in the installation height and installation width of the flow channels feeding around the transfer pipe.
Preferably, a greater part of the exhaust gas flow continues to flow completely around the transfer pipe and enters it through the main intake opening. A preferably smaller part of the exhaust gas flow flows in laterally through the auxiliary intake openings, where it assists the formation of the vortex, in particular the double vortex.
Incidentally, preferably all characteristics, including those of the at least one baffle element preferably provided in this region, which have been described previously for the intake opening, in particular for the single intake opening, are realized for the main intake opening. Accordingly, the exemplary embodiment described here preferably differs from the previously described exemplary embodiments only in that at least one auxiliary intake opening, preferably two auxiliary intake openings, is/are provided in addition.
Preferred is an exhaust gas system, in which the at least one auxiliary intake opening has at least one flow guide element, by means of which the exhaust gas can be guided substantially tangentially into the transfer pipe. As a result, the formation of the swirl, in particular of the double vortex, is assisted in a particularly favorable manner, as the exhaust gas is guided tangentially through the at least one auxiliary intake opening into the transfer pipe and in this respect is endowed with a tangential speed component. At the same time, the flow guide element is preferably designed as an outwardly and/or inwardly—viewed in the radial direction, that is to say in a direction lying perpendicular to the longitudinal direction—curved region of the sleeve surface of the transfer pipe. Particularly preferably, both an outwardly and inwardly curved region of the sleeve surface is provided along the whole longitudinal extension of the auxiliary intake opening, thus resulting in a particularly favorable flow guidance in the tangential direction.
The very efficient mixing and also vaporization of the reducing agent in the region of the intake opening and of the transfer pipe enables a separate mixer for distributing the reducing agent injected into the exhaust gas to be dispensed with. This also avoids a pressure loss that would otherwise be caused by the mixer, which is advantageous as a whole for the exhaust gas system and in particular downstream exhaust gas aftertreatment elements.
Preferably, the whole geometric embodiment of the exhaust gas system, in particular the cross-sectional dimensions of the transfer pipe and the dimensions of the intake opening, are chosen such that a swirl rate of at least 0.3 referred to each individual vortex of the double vortex is achieved for the exhaust gas swirl in the transfer pipe. In particular, the geometry of the exhaust gas system is designed depending on a capacity of the internal combustion engine such that an inlet swirl rate of at least 0.3 is achieved.